An introduction to QUANTUM GIS (QGIS) and web mapping: Session 1

---

Date and Place: Pompeu Fabra University, 4-6 April 2016

Instructors: Juan Galeano & Antonio López Gay

---

Brief introduction

What is a GIS? (1)

GIS stands for Geographical Information System

A GIS consists of:

• Digital Data: the geographical information that you will view and analyse using computer hardware and software.

• Computer Hardware: computers used for storing data, displaying graphics and processing data.

• Computer Software: computer programs that run on the computer hardware and allow you to work with digital data. A software program that forms part of the GIS is called a GIS Application.

With a GIS application you can open digital maps on your computer, create new spatial information to add to a map, create printed maps customised to your needs and perform spatial analysis.

What is QGIS

QGIS is a user friendly Open Source Geographic Information System (GIS) licensed under the GNU General Public License. QGIS is an official project of the Open Source Geospatial Foundation (OSGeo).

Why QGIS?

As information becomes increasingly spatially aware, there is no shortage of tools able to fulfill some or all commonly used GIS functions. Why should anyone be using QGIS over some other GIS software package?

Here are only some of the reasons:

• It’s free: Installing and using the QGIS program costs you a grand total of zero money. No initial fee, no recurring fee, nothing.

• It’s Open Source: If you need extra functionality in QGIS, you can do more than just hope it will be included in the next release. You can sponsor the development of a feature, or add it yourself if you are familiar with programming.

• It’s constantly developing: Because anyone can add new features and improve on existing ones, QGIS never stagnates. The development of a new tool can happen as quickly as you need it to.

• Extensive help and documentation is available: If you’re stuck with anything, you can turn to the extensive documentation, your fellow QGIS users, or even the developers.

• Cross-platform: QGIS can be installed on MacOS, Windows and Linux.

Download and install QGIS in your computer

QGIS can by can be downloaded from its web page: http://www.qgis.org/en/site/forusers/download.html

What is a shapefile? (2)

The shapefile format is a popular geospatial vector data format for geographic information system (GIS) software. A shapefile is composed by

Mandatory files

• .shp: shape format; the feature geometry itself
• .shx: shape index format; a positional index of the feature geometry to allow seeking forwards and backwards quickly
• .dbf: attribute format; columnar attributes for each shape, in dBase IV format

Other files

• .prj: projection format; the coordinate system and projection information, a plain text file describing the projection using well-known text format
• .sbn and .sbx: a spatial index of the features
• .fbn and .fbx: a spatial index of the features that are read-only
• .ain and .aih:an attribute index of the active fields in a table
• .ixs: a geocoding index for read-write datasets
• .mxs: a geocoding index for read-write datasets (ODB format)
• .atx: an attribute index for the .dbf file in the form of shapefile.columnname.atx (ArcGIS 8 and later)
• .shp.xml: geospatial metadata in XML format, such as ISO 19115 or other XML schema
• .cpg: used to specify the code page (only for .dbf) for identifying the character encoding to be used
• .qix: an alternative quadtree spatial index used by MapServer and GDAL/OGR software

Where to get a shapefile?

There are several institutions/organizations devoted to provide geographical information. This is a incomplete but useful list to start:

GLOBAL ADMINISTRATIVE AREAS, Boundaries without Limits: GADM is a spatial database of the location of the world’s administrative areas (or adminstrative boundaries) for use in GIS and similar software. Administrative areas in this database are countries and lower level subdivisions such as provinces, departments, bibhag, bundeslander, daerah istimewa, fivondronana, krong, landsvæðun, opstina, sous-préfectures, counties, and thana. GADM describes where these administrative areas are (the “spatial features”), and for each area it provides some attributes, such as the name and variant names.

EUROSTAT GEODATA: NUTS, European Countries: Administrative units / Statistical units / NUTS / Urban Audit / Countries / Census / Communes

CENTRO NACIONAL DE INFORMACIÓN GEOGRÁFICA: The Download Center is a website from the National Center for Geographic Information (CNIG) where free downloads of geographic data files generated by the National Geographic Institute (IGN) can be made. Provided this information is accessible in accordance with Orden FOM/2807/2015 , of December 18th (BOE dated December 26th, 2015), which establishes the policy for the public diffusion of geographic data generated by the Directorate General of the National Geographic Institute.

DIVA-GIS: DIVA-GIS is developed by Robert Hijmans. Previous versions were co-developed with Edwin Rojas, Mariana Cruz, Rachel O’Brien, and Israel Barrantes. Our objective is to develop a free, and simple but versatile GIS program, that is particularly useful for studying the distribution of biodiversity. Countries / Different administrative levels.

NOMECALLES, Comunidad de Madrid: Shapefiles Madrid (Autonomous Community, Municipalities, census tracts, others).

INSTITUTO DE ESTADÍSTICA Y CARTOGRAFÍA DE ANDALUCIA: (Autonomous Community, Municipalities, census tracts, others).

CARTOBCN: Shapefiles of the municipality of Barcelona (Districts / Neighborhoods / Census tracts).

INSTITUT GEOLOGIC i CARTOGRÀFIC DE CATALUNYA: Shapefiles of Catalonia (Comarques / Municipalities / Census tracts).

What is a Coordinate Reference System (CRS)? (3)

A spatial reference system (SRS) or coordinate reference system (CRS) is a coordinate-based local, regional or global system used to locate geographical entities.

World’s most famous GIS: Google Maps

---

QGIS Desktop and Browser

The QGIS Browser is a panel in QGIS that lets you easily navigate in your filesystem and manage geodata. You can have access to common vector files (e.g., ESRI shapefiles or MapInfo files), databases (e.g., PostGIS, Oracle, SpatiaLite or MS SQL Spatial) and WMS/WFS connections. You can also view your GRASS data (to get the data into QGIS, see GRASS GIS Integration). ***

Excercise 1: Read shapefiles into QGIS and manipulate features

---

1. Download shapefiles from Spain from gadm
2. General manipulation of a layer in QGIS
   • 2.1 Read the shapefile of Spain by Autonomous Communities
   • 2.2 Save a layer as a ESRI shapefile
   • 2.3 Open Attribute table
   • 2.4 Identify Features
   • 2.5 Select Features
   • 2.6 Toogle Editing
     • 2.6.1 Delete Features (Ceuta and Melilla)
     • 2.6.2 Move Features (Canary Islands)

1. Download shapefiles from Spain from gadm.org

2. General manipulation of a layer in QGIS

2.1 Read data into QGIS

QGIS allows us to work with all kind of spatial data (vectors, raster images, spatialite, etc.). To read a shapefile into QGIS we

1. request to add a vector layer from the Layer tab,

2. look for the shapefile (ESP_adm2.shp in this case) and click the Open button:

NOTE: alternatively, we can simply look for the shapefile on the QGIS browser and dragged into the Desktop.

2.2 Save a layer as a ESRI shapefile

As we want to edit a layer (delete and move features) first we save a copy of the original shapefile.

QGIS allows us to save a layer in multiple spatial formats. To save a layer as an ESRI shapefile we

1. select the layer to save on Layer panel, click on the right buttom of the mouse and Save As.

2. Select ESRI Shapefile on the Format tab and

3. Browse to select the output files name and location. Ok

2.3 Open Atributte table

Data associated with the shapefile can be access from the Open Attribute table tab.

2.4 Identify Features

The Identify features tab allows us access data associated with each of the elements (polygons in this case) of the shapefile.

2.5 Select Features

The Select features tab allows us to select features by area or by clicking on them.

2.6 Toogle Editing

In order to Delete, Move, re-draw ,etc. a feature from a layer, first we activate the Toogle Editing tab.

2.6.1 Delete Features (Ceuta and Melilla)

After turning on the editing mode, select the feature/s to delet and click on the delete (trash) tab. Or simply click the backspace key on your keyboard.

2.6.2 Move Features (Canary Islands)

After turning on the editing mode, select the feature/s to move click on the Move Feature(s) tab and then place the selection wherever you want.

Lastly, turn off the editing mode and save changes.

---

---

Excercise 2: Create new layers and shapefiles

---

1. Read the shapefile CAT_2014_SC into QGIS
2. Create new layers
   • 2.1 Duplicate a layer
   • 2.2 Aggregate geographical levels
   • 2.3 Split a vector layer
   • 2.4 Merge shapefiles to one

2.1 Duplicate a layer

To duplicate a layer

1. select the layer to duplicate on Layer panel,

2. click on the right buttom of the mouse and Duplicate.

2.2 Aggregate geographical levels (Dissolve)

We have loaded a shapefile of Catalonia by census tracts in 2014. Within the attributes of the shapefile there are two columns (MUNICPI and PROV) by which we can aggregate census census tracts. So, we will create two new layers (and corresponding shapefiles): one of Catalonia by municipalities (947) and by provinces (4). In order to perform this task we

1. Click on the Vector tab and within the Geoprocessing tools select Dissolve.

2. Select an input vector layer (CAT_2014_SC in this case) and a Dissolve field (MUNICIPI).

3. Browse to select the output files name and location. Ok

Repeat the same operation but dissolving the layer of census tracts by provinces. Please, name your new layer and shapefile CAT_2014_PROV.

2.3 Split a vector layer

Now we split our new layer (CAT_2014_MUN) of Catalonia by municipalities into four shapefiles (1 for each catalan province). In order to perform this task we

1. Click on the Vector tab and within Data Management Tools select Split Vector Layer.

2. Browse to select the output folder. Ok

2.4 Merge shapefiles to one

With QGIS is really easy to merge several shapefiles to one. In order to perfom this task:

1. Create a new folder with the shapefiles to merge,

2. Click on the Vector tab and within Data Management Tools select Merge Shapefiles to one.

3. Browse to select an input directory (Folder from step 1) and Browse to select the output files name and location. Ok.

---

---

Excercise 3: Add new columns to layer properties

---

1. Add new columns to layer properties
   • 1.1 Add Geometry Columns
   • 1.2 Basic computation: the field calculator
     • 1.2.1 Add a column with the percentage of foreign-born population by census tract
     • 1.2.2 Add a column with the population density by census tract

1.1 Add Geometry Columns

If we need to know the area and perimiter of each polygon of a layer

1. Click on the Vector tab and within Geometry Tools select Export/Add Geometry Columns.

2. Check the Save to new shapefile box and

3. Browse to select the output files name and location. Ok.

1.2 Basic computation: the field calculator

If we need some computation between extisting variables

1. Open the Attribute Table

2. Turn on the editing mode,

3. Opent the Field Calculator

4. Name the new variable

5. Select the field type and length

---

---

Excercise 4: Join data to shapefile

---

1. Create a dbf file
2. Read a .cvs file into QGIS
3. Join data from two layers
4. Basic Statistics of a variable

1. Create a dbf file

Recall: .dbf: attribute format; columnar attributes for each shape, in dBase IV format.

The easiest way to create a .dbf file is to download and install Open Office, read a .csv into the OpenOffice Calc and save it as a .dbf file.

2. Read a .cvs file into QGIS

The most common situation is not to found a shapefile with the data we want to represent on its .dbf file. So let’s see how to read a *csv file into QGIS and Join data to shapefile.

To read a csv into QGIS we

1. request to add Delimited Text Layer from the Layer tab,

2. look for the csv (DATOS_CAT_2014.csv in this case)

3. check the No Geometry (attribute only table) checkbox. Ok

NOTE: alternatively, we can simply look for the .csv file on the QGIS browser and dragged into the Desktop.

3. Join data from two layers

In order to join data to a layer,

1. Double-click on the shape layer on the Layer Panel and open the Layer Properties dialogue box

2. On the Joins tab add using the + symbol,

3. Assign a Join Layer (you data, .csv file)

4. Assign Join and Target field and

5. Choose which fields are joined. Ok

---

---

Excercise 5: Create a choropleth map

---

1. Split the CAT_2014_SC layer by municipalities (MUNICIPI). (Create a new folder within the SHAPEFILES folder of the course)
2. Read the shapefile **CAT_2014_SC_MUNICIPI__080193** into QGIS.
3. Add a column (PROPEXT) with the proportion (expressed as percentage) of foreign-born population in each census tract (1061). Decimal number of length 4. (e.g. 21.55).
4. Create a chroropleth map.

Greate a choropleth map

A choropleth map is a thematic map in which areas are shaded or patterned in proportion to the measurement of the statistical variable being displayed on the map, such as population density or per-capita income (4).

Recall previous exercises to perfom steps 1, 2 and 3.

4. Create a chroropleth map

1. Double-click on the shape layer on the Layer Panel and open the Layer Properties dialogue box

2. Select Graduated

3. Select the PROPEXT column,

4. Change the color ramp to oranges,

5. On Mode select Pretty Breaks and click on Classify

6. Click on symbol, Simple fill and set the board width to 0.160000,

7. Apply and Ok.

It seems you have a first map!!! Congrats!!!!

---

Excercise 6: Export maps as images or pdf files: The print Composer

---

The Print Composer With the Print Composer (5) you can create nice maps and atlasses that can be printed or saved as PDF-file, an image or an SVG-file. This is a powerfull way to share geographical information produced with QGIS that can be included in reports or published.

The Print Composer provides growing layout and printing capabilities. It allows you to add elements such as the QGIS map canvas, text labels, images, legends, scale bars, basic shapes, arrows, attribute tables and HTML frames. You can size, group, align, position and rotate each element and adjust the properties to create your layout. The layout can be printed or exported to image formats, PostScript, PDF or to SVG (export to SVG is not working properly with some recent Qt4 versions; you should try and check individually on your system). You can save the layout as a template and load it again in another session. Finally, generating several maps based on a template can be done through the atlas generator.

1. Open the Print Composer
2. Add a new map
3. Add arrow or line
4. Add scalebar
5. Add Label
6. Add legend

• 6.1 Edit legend (Item Properties)
• 6.2 Define dpi resolution

6. Save map as image or pdf file

1. Open the Print Composer

2. Add a new map

3. Add arrow or line

4. Add scalebar

5. Add Label

6. Add legend

6.1 Edit legend (Item Properties)

1. On the Item properties tab go to Legend items,

2. Un-check the Auto Update,

3. Edit the legend by items.

6.2 Define dpi resolution

1. On the Composition tab go to Export settings,

2. Set resolution on 300 dpi.

6.2 Save map as image or pdf file

1. Export as image

2. Export as pdf

---

Excercise 7: Create an Atlas: The Altlas Composer

---

1. Read the shapefile CAT_2014_DISTRICTES into QGIS.
2. Set the polygon fill of layer CAT_2014_DISTRICTES to transparent.
3. set the board width to 0.460000
4. Open a new print composer.
5. Create an Atlas.
6. Save each element of the Atlas as a .png file.

Recall previous exercises to perfom steps 1, 2, 3 and 4.

5. Create an Atlas

1. On the Atlas Generation tab check the Generate an Atlas box,

2. Coverage Layer: CAT_2014_DISTRICTES

3. Switch to the Item Properties Tab and check the Controled by Atlas box.

4. Preview Atlas

Recall previous exercises to perfom steps 6.

---

Excercise 8: Consolidation task 1

---

1. Open a new project

On the folder CONSOLIDATION TASK1 you have the 36 shapefiles of the municipalities of the Metropolitan Area of Barcelona by census tracts in 2014.

            CAT_2014_SC_MUNICIPI__080155
            CAT_2014_SC_MUNICIPI__080193
            CAT_2014_SC_MUNICIPI__080207
            CAT_2014_SC_MUNICIPI__080543
            CAT_2014_SC_MUNICIPI__080569
            CAT_2014_SC_MUNICIPI__080689
            CAT_2014_SC_MUNICIPI__080728
            CAT_2014_SC_MUNICIPI__080734
            CAT_2014_SC_MUNICIPI__080771
            CAT_2014_SC_MUNICIPI__080898
            CAT_2014_SC_MUNICIPI__081017
            CAT_2014_SC_MUNICIPI__081234
            CAT_2014_SC_MUNICIPI__081252
            CAT_2014_SC_MUNICIPI__081265
            CAT_2014_SC_MUNICIPI__081574
            CAT_2014_SC_MUNICIPI__081580
            CAT_2014_SC_MUNICIPI__081691
            CAT_2014_SC_MUNICIPI__081803
            CAT_2014_SC_MUNICIPI__081944
            CAT_2014_SC_MUNICIPI__081960
            CAT_2014_SC_MUNICIPI__082009
            CAT_2014_SC_MUNICIPI__082042
            CAT_2014_SC_MUNICIPI__082055
            CAT_2014_SC_MUNICIPI__082114
            CAT_2014_SC_MUNICIPI__082172
            CAT_2014_SC_MUNICIPI__082212
            CAT_2014_SC_MUNICIPI__082444  
            CAT_2014_SC_MUNICIPI__082457
            CAT_2014_SC_MUNICIPI__082520
            CAT_2014_SC_MUNICIPI__082634
            CAT_2014_SC_MUNICIPI__082665  
            CAT_2014_SC_MUNICIPI__082824
            CAT_2014_SC_MUNICIPI__082896
            CAT_2014_SC_MUNICIPI__083015
            CAT_2014_SC_MUNICIPI__089045
            CAT_2014_SC_MUNICIPI__089058

2. Merge shapefiles to one. Name the new layer and shapefile AMB_SC.

3. Create a new layer with the municipal boundaries of the AMB. Name it AMB_MUNICIPIS.

4. Delete the columns “PROPEXT”, “Totalpop” y “Totalext” from the attibute table of the layer AMB_SC.

5. Read the .csv CAT_2014_DATOS into QGIS.

6. Join the columns “Totalpop” and “Totalext” from CAT_2014_DATOS to the AMB_SC layer.

7. Add the following colums to the the attibute table of the layer AMB_SC:
   • 7.1 “PROPEXT”: Totalpop/Totalext*100 (Output fiel Type: Decimal (Presicion 4))
   • 7.2 “AMBPROPEXT”: 18.94704 (Output fiel Type: Decimal (Presicion 4))
   • 7.3 “LQ_EXT”: PROPEXT/AMBPROPEXT (Output fiel Type: Decimal (Presicion 4))
   • 7.4 “AMB”: concat(‘AMB’) (Output fiel Type: Text (string))

8. Create a new layer with the boundaries of the AMB. Name it AMB_CONTORNO

9. Create a chorolplet map over the variable “LQ_EXT” with 7 intervals (as in the following image). Color ramp: Spectral, invert
   • 9.1 Overlay the layer AMB_MUNICIPIS with transparent fill. (play with the boarder width)
   • 9.2 Overlay the layer AMB_CONTORNO with transparent fill. (play with the boarder width)

10. Export you map as an image (300 dpi) and as a PDF.

Expected Outcome

Sources:

1. A Gentle Introduction to GIS

2. SHAPEFILE

3. Coordinate Reference System

4. Choropleth map

5. Print Composer